Shot peening represents a known example of a surface modification process that is used for enhancing the fatigue strength of metallic materials such as the structural members used in aircraft and automobiles and the like (see Non Patent Citation 1). Shot peening is a method in which, by blasting countless particles having a particle size of around 0.8 mm (the shot material) together with a stream of compressed air onto the surface of a metallic material, the hardness of the metallic material surface is increased, and a layer having compressive residual stress is formed at a certain depth.
Furthermore, other techniques such as flapper peening and cold working are also used as methods of enhancing the fatigue strength of a metallic material.
Non Patent Citation 1: T. Dorr and four others, “Influence of Shot Penning on Fatigue Performance of High-Strength Aluminum- and Magnesium Alloys”, The 7th International Conference on Shot Peening, 1999, Institute of Precision Mechanics, Warsaw, Poland. Internet <URL: http://www.shotpeening.org/ICSP/icsp-7-20.pdf>